1. Field of the Invention
The present invention relates generally to medical surgical devices, systems, and methods. More specifically, the invention relates to devices, systems and methods for facilitating knee surgery procedures, in particular, knee replacement procedures.
2. Description of the Related Art
The knee is generally defined as the point of articulation of the femur with the tibia. Structures that make up the knee include the distal femur, the proximal tibia, the patella, and the soft tissues within and surrounding the knee joint, the soft tissues including the ligaments of the knee. The knee is generally divided into three compartments: medial (the inside part of the knee), lateral (the outside part of the knee), and patello-femoral (the joint between the kneecap and the femur). The medial compartment comprises the medial joint surfaces of the femur, tibia, and the meniscus wedged therebetween. The lateral compartment comprises the lateral joint surfaces of the femur, tibia, and the meniscus wedged therebetween. The patellofemoral compartment comprises the joint between the undersurface of the kneecap or patella and the femur. Four ligaments are especially important in the stability, alignment and functioning of the knee—the anterior cruciate ligament, the posterior cruciate ligament, the medial collateral ligament, and the lateral collateral ligament. In an arthritic knee, protective cartilage at the point of articulation of the femur with the tibia is often worn away, allowing the femur to directly contact the tibia. This bone-on-bone contact can cause significant pain, discomfort, and disability for a patient and will often necessitate knee replacement or knee arthroplasty.
Knee arthroplasty involves replacing the diseased and painful joint surface of the knee with metal and plastic components shaped to allow natural motion of the knee. Knee replacement may be total or partial. Total knee replacement surgery, also referred to as total knee arthroplasty (“TKA”), involves a total replacement of the distal end of the femur, the proximal end of the tibia, and often the inner surface of the patella with prosthetic parts. Cuts are made on the distal end of the femur and the proximal end of the tibia. Prosthetic parts are then attached. The prosthetic parts create a stable knee joint that moves through a wide range of motion. The replacement of knee structures with prosthetic parts allows the knee to avoid bone-on-bone contact and provides smooth, well-aligned surfaces for joint movement.
In knee replacement surgeries, it is often vital to restore the mechanical alignment of the knee, i.e., the proper alignment of the mechanical axes of the femur and tibia with each other. Many methods and devices currently are used to restore the mechanical alignment of the leg. These methods and devices are typically used during Total Knee Replacement surgery and include alignment rods, e.g., intramedullary and extramedullary rods, surgical navigation systems, and CT and or MRI based “bone morphing” or “shape-fitting” technologies. Generally, empirical anatomical landmarks are used in these methods. These anatomical landmarks are either directly/mechanically observed intra-operatively, or indirectly relied upon, serving as the foundation of a computer generated reference method. Reference geometry and physical or virtual measurements are often used to ultimately align bone-cutting guides or templates which facilitate bone resections (made with a surgical saw blade). These bone resections will typically properly orient a knee prosthesis in the correct location/alignment. Generally, none of these methods directly take the condition or tendencies of the soft-tissue structures, such as the lateral collateral and medial collateral ligaments, about the knee into consideration.
Historically, surgeons performing total knee replacement surgery in the late 1970s and early 1980s would typically first resect the proximal tibia, creating a flat surface perpendicular to the shaft of the tibia. The leg was then brought to extension. Spacer blocks were shoved between the resected tibia and the uncut distal femur. The spacer blocks were selected from various thicknesses in order to distract the knee joint space to the extent the ligaments about the knee were somewhat taut. Once the knee joint was distracted to that taut condition, a distal femoral cutting guide was positioned in a way to yield a distal femoral bone cut parallel to the tibial cut. It was believed that a distal femoral bone cut, using this method of distracting the joint space between the tibia and femur, would yield proper alignment of the mechanical axis of the leg. This method would often prove successful as practiced by a skilled surgeon and in the case of “passive deformities” of the knee. However, the distraction method would typically not have any accurate means of determining ligament forces between the medial side of the knee and/or the lateral side of the knee. As such, proper alignment would often not be restored. Additionally, the method of first making a proximal tibial bone resection and then making a distal femoral bone resection parallel to the tibial bone resection did not restore proper alignment of the leg in the case of “fixed deformities” of the knee. The case of “fixed deformities” of the knee would otherwise require ligament releases to restore proper alignment of the knee. Accordingly, many early knee replacement surgeons determined that the tibial bone resection and the distal femoral bone resections should be made independent of each other.
As technology has advanced, including the introduction of CT scanners and MRI technology, the thought of computerized bone morphing has gained popularity as a means to accurately place cutting guides. The cutting guides, in turn, are be used in efforts to place prosthetic knee implants in a position in which the knee is properly aligned. Early studies have not found these bone morphing technologies always accurate, reporting proper alignment of the leg was not restored. However, a proper patient selection, e.g., patients with mild, passive deformities of the knee, might be viable candidates for bone morphing technology, assuming those patients/deformities could be properly corrected by simple anatomical referencing, as determined by a CT or MRI scan.
However, bone morphing technology is often costly, requiring a CT or MRI scan to determine any given patient's anatomy. Electronic images from such scans must be “filtered” by a computer technician. The “filtered” scan data must be electronically conveyed to some type of fabrication machine, such as a CNC Machining Center or a Rapid Prototype Machine. Ultimately, “shape-matching” and “patient specific” cutting guides must be produced and delivered into surgery.
As such, there is a clear need for systems, devices, and methods of knee surgery that can help surgeons quickly, accurately, and cost-effectively position the distal femoral cutting guide, thus restoring proper alignment and soft-tissue balance of the leg during total knee replacement surgery.
Non-patent literature which may be of interest may include: Murray, David G., “Variable Axis™ Total Knee Surgical Technique,” Howmedica Surgical Techniques, Howmedica Inc. 1977; Mihalko, W H et al., “Comparison of Ligament-Balancing Techniques During Total Knee Arthroplasty,” Jnl. Bone & Jt. Surg., Vol. 85-A Supplement 4, 2003, 132-135; Eckhoff, D G et al., “Three-Dimensional Morphology and Kinematics of the Distal Part of the Femur Viewed in Virtual Reality, Jnl. Bone & Jt. Surg., Vol. 85-A Supplement 4, 2003, 97-104; and Ries, M D, et al., “Soft-Tissue Balance in Revision Total Knee Arthroplasty,” Jnl. Bone & Jt. Surg., Vol. 85-A Supplement 4, 2003, 38-42. Patents of interest may include U.S. Pat. Nos. 4,501,266; 4,646,729; 4,703,751; 4,841,975; 5,116,338; 5,417,694; 5,540,696; 5,597,379; 5,720,752; 5,733,292; 5,800,438; 5,860,980; 5,911,723; 6,022,377 and 6,758,850. Patents applications of interest may include co-assigned U.S. patent application Ser. No. 10/773,608, now U.S. Pat. No. 7,442,196, entitled “Dynamic Knee Balancer”; Ser. No. 10/973,936, now U.S. Pat. No. 7,578,821 entitled “Dynamic Knee Balancer with Pressure Sensing”; Ser. No. 11/149,944 now U.S. Patent Publication Application No. 2005/0267485 A1 entitled “Dynamic Knee Balancer with Opposing Adjustment Mechanism”; 61/090,535 entitled “Sensing Force During Partial and Total Knee Replacement Surgery”; and 61/107,973 entitled “Dynamic Knee Balancing for Revision Procedures”, the entire contents of each of which are incorporated herein by reference.